CVE-2018-5166 in Firefox
Summary
by MITRE
WebExtensions can use request redirection and a "filterReponseData" filter to bypass host permission settings to redirect network traffic and access content from a host for which they do not have explicit user permission. This vulnerability affects Firefox < 60.
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Analysis
by VulDB Data Team • 03/11/2023
This vulnerability in Firefox represents a significant bypass of the browser's security model that undermines the fundamental principle of host permissions within the WebExtensions framework. The flaw allows malicious extensions to circumvent the permission system that should restrict access to specific hosts, creating a pathway for unauthorized network traffic redirection and content access. The vulnerability specifically affects versions prior to Firefox 60, indicating it was present in the browser for several years and likely exploited in the wild before being addressed. The security implications are particularly severe because it directly violates the core security boundary that separates user permissions from extension capabilities, potentially enabling data exfiltration, man-in-the-middle attacks, and unauthorized access to sensitive resources.
The technical mechanism behind this vulnerability involves the manipulation of network request handling through two key components: request redirection capabilities and the filterResponseData filter functionality within the WebExtensions API. Extensions can utilize these features to intercept and modify network traffic in ways that bypass the normal host permission checks that should occur when an extension attempts to access resources from domains other than those explicitly permitted by the user during installation. The filterResponseData filter, when combined with request redirection, creates a scenario where an extension can effectively mask its true network activity, making it appear as though it's accessing content from a permitted host while actually redirecting traffic to unauthorized destinations. This represents a sophisticated bypass that exploits the complex interaction between browser security boundaries and extension APIs.
The operational impact of this vulnerability extends beyond simple permission bypass to create potential for extensive data collection and unauthorized access to sensitive information. Attackers could leverage this flaw to redirect users' traffic to malicious servers, harvest credentials from protected domains, or access private information without user knowledge or consent. The vulnerability is particularly dangerous in environments where users trust extensions with broad permissions, as it allows extensions to silently expand their access beyond the scope of user expectations. The attack surface is broad because the flaw affects the core networking capabilities of Firefox, potentially enabling extensions to access any host on the internet regardless of user-permission settings, which could include corporate networks, personal accounts, or sensitive government resources.
Mitigation strategies for this vulnerability require immediate updates to Firefox versions that include the patched implementation of the WebExtensions security model. Organizations should ensure all Firefox installations are updated to version 60 or later where the vulnerability has been addressed through enhanced permission checking mechanisms. Security administrators should also implement monitoring for unusual network traffic patterns that might indicate redirection activities, though this is a challenging mitigation given the stealthy nature of the attack. The fix implemented by Mozilla addresses the specific interaction between request redirection and response data filtering by strengthening the host permission validation process, ensuring that extensions cannot bypass these security checks through API manipulation. This vulnerability highlights the importance of maintaining up-to-date browser software and demonstrates how complex API interactions can create unexpected security gaps in modern browser architectures. The issue aligns with CWE-284 Access Control and ATT&CK techniques related to privilege escalation and credential access, emphasizing the need for comprehensive security testing of browser extension APIs.
The broader implications of this vulnerability extend to the entire WebExtensions ecosystem, as it demonstrates how seemingly legitimate API features can be exploited to create security bypasses. This flaw serves as a reminder of the complexity involved in securing browser extension environments where extensions have significant access to user data and network communications. The vulnerability also underscores the importance of proper API design and the need for robust security boundaries even within trusted extension environments. Organizations should consider implementing additional security measures such as extension whitelisting, network monitoring, and user education about extension permissions to mitigate risks associated with such vulnerabilities. The incident represents a critical lesson in the ongoing battle between browser functionality and security, where feature-rich APIs must be carefully designed to prevent unintended security consequences that could compromise user privacy and data protection.